Apparatus has previously been described--see U.S. Pat. No. 4,530,694, Kobler, the disclosure of which is incorporated by reference--to rotate sheets or packages of sheets about 90.degree. in the major plane of the sheets. Sheets may have to be rotated when they have been folded. Due to the fold, one edge will be thicker than the other and, upon stacking of folded products, the incremental thickness at the folds may add; when a certain height of a stack is reached, the stack becomes unstable and tends to tip over.
The known apparatus merely permits folded products to rotate by 90.degree. so that, upon alternate stacking of rotated and original, non-rotated products, a stack will be formed with two sides of essentially uniform height. Such a stacking arrangement is substantially better than a stack of folded products in which none of them are rotated; yet, the stability of such a stack is not sufficient after a predetermined height thereof has been reached. Opening of the stacked products is only possible if the stacked products contain an additional fold-in sheet, to separate the individual sheet elements which have been folded.
Apparatus as described to rotate predetermined folded products, for example all the odd folded products within a sequence thereof, is insufficient if the folded products, or packages thereof, have two folds, that is, have a longitudinal fold and a cross fold extending at right angles to the longitudinal fold. If such folded products are supplied to the known apparatus, compensation for height differences would be possible; opening of the folded products, however, at the fold sheets would not be possible without providing an additional fold-in flap on one of the sheet elements. The following patents and application, assigned to the assignee of the present invention, the disclosures of which are hereby incorporated by reference, relate to subject matter of this application:
U.S. Pat. No. 4,840,365, Kobler et al PA0 U.S. Pat. No. 4,807,865, Kobler et al PA0 U.S. Pat. No. 4,871,159, Petersen PA0 U.S. Ser. No. 07/519,119, filed May 4, 1990, Kobler et al, now U.S. Pat. No. 5,110,116.